Electroless plating technique has been a well-developed plating technology. Currently, this technique is used mostly for treating objects other than semiconductor wafers. Accordingly, no strict demand is required regarding the uniformity of the thickness of plated film. Besides, this technique is also not designed specifically for plating micro-size via holes.
Recently, with the rapid development of semiconductor technology, the electroless plating technique becomes very popular for plating metal film on semiconductor wafers, such as those of plating a Au or Cu metal film on backside via holes of silicon chips or gallium arsenide chips.
Therefore, there is an increasing demand for the thickness uniformity of the plated film and the capability of plating of micro-size via holes or trenches. However, conventional electroless plating techniques cannot meet the aforementioned requirements for plating semiconductor wafers.
In order to meet the demands for semiconductor technology, the conventional electroless plating technique should be improved. One possible way is to develop a novel formula for the electrolyte. The other way is to modify the apparatus used for electroless plating. The present invention is aimed to modify current electroless plating apparatus in order to make the plating of wafers optimum.